import { db } from '../db/index.js';
import { listHosts } from '../hosts/index.js';
import { protectedWork } from '../autoscaling/snapshot.js';
import { freshStatusTimestamp } from '../../server-freshness.js';
import { listServers, type ServerRow } from './servers.js';
import { observationReader } from './status.js';
import type { ScriptRow } from './scripts.js';

const games = ['t5', 't6'] as const;
type Game = (typeof games)[number];
type Counts = Partial<Record<Game, number>>;

export function parseBetaInstanceCounts(value: unknown): Counts {
    if (!value || typeof value !== 'object' || Array.isArray(value) || !Object.keys(value).length) {
        throw new Error('instancesPerGame must contain at least one game and instance count');
    }
    const counts: Counts = {};
    for (const [game, count] of Object.entries(value)) {
        if (
            !games.includes(game as Game) ||
            !Number.isSafeInteger(count) ||
            count < 1 ||
            count > 1000
        ) {
            throw new Error('Instance counts must be integers from 1 to 1000 for t5 or t6');
        }
        counts[game as Game] = count;
    }
    return counts;
}

function matches(script: ScriptRow, server: ServerRow): boolean {
    return (
        !script.scope_type ||
        !script.scope_value ||
        (script.scope_type === 'game' ? server.game : server.map) === script.scope_value
    );
}

/** Choose at submission time using the same fresh observations shown in Fleet. */
export function selectBetaServers(scripts: ScriptRow[], instancesPerGame: unknown): string[] {
    const counts = parseBetaInstanceCounts(instancesPerGame),
        observe = observationReader(),
        now = Date.now();
    const hosts = new Map(listHosts().map((host) => [host.id, host]));
    const busy = new Set(
        (
            db()
                .prepare(
                    `SELECT server FROM server_deployments WHERE server_deleted_at IS NULL
        AND (state IN ('queued','waiting','running','awaiting-health','interrupted')
            OR (action IN ('destroy','rebuild') AND state = 'failed'
                AND stage IN ('Stopping and removing container','Removing server files and registry')))`
                )
                .all() as { server: string }[]
        ).map((row) => row.server)
    );
    const candidates = listServers()
        .flatMap((server) => {
            if (
                !counts[server.game as Game] ||
                server.desired_state === 'stopped' ||
                busy.has(server.name) ||
                !scripts.some((script) => matches(script, server)) ||
                protectedWork(server.name)
            )
                return [];
            const host = server.host_id ? hosts.get(server.host_id) : null;
            if (server.host_id && (!host?.connected || host.mode !== 'active' || host.decommission))
                return [];
            const observation = observe(server);
            if (
                observation.health !== 'online' ||
                observation.last_players === null ||
                !freshStatusTimestamp(observation.last_seen_at, now)
            )
                return [];
            // An occupied RCON observation must not rank as empty just because a
            // competing telemetry report claims zero players.
            const rconPlayers =
                freshStatusTimestamp(server.last_seen_at, now) &&
                (!observation.telemetry_after ||
                    Date.parse(server.last_seen_at!) > Date.parse(observation.telemetry_after))
                    ? (server.last_players ?? 0)
                    : 0;
            return [{ server, players: Math.max(observation.last_players, rconPlayers) }];
        })
        .sort((a, b) => a.players - b.players || a.server.name.localeCompare(b.server.name));

    for (const game of games) {
        const available = candidates.filter((candidate) => candidate.server.game === game).length;
        if ((counts[game] ?? 0) > available) {
            throw new Error(
                `${game.toUpperCase()} needs ${counts[game]} available instances, but only ${available} have fresh status and no pending work. Reduce the count or retry when more servers are available.`
            );
        }
    }
    for (const script of scripts) {
        if (!candidates.some((candidate) => matches(script, candidate.server))) {
            throw new Error(
                `${script.name}: no available server in the requested games matches this file's scope.`
            );
        }
    }

    // Map scopes need a representative even when the least populated servers
    // all run the same map. Reserve enough remaining slots for every map.
    const requiredMaps = new Set(
        scripts.filter((script) => script.scope_type === 'map').map((script) => script.scope_value!)
    );
    function canComplete(remaining: typeof candidates, slots: Counts, maps: Set<string>): boolean {
        const options = new Map<string, Set<Game>>();
        for (const game of games) {
            if (
                remaining.filter((candidate) => candidate.server.game === game).length <
                (slots[game] ?? 0)
            )
                return false;
        }
        for (const map of maps) {
            const choices = new Set(
                remaining
                    .filter(
                        (candidate) =>
                            candidate.server.map === map &&
                            (slots[candidate.server.game as Game] ?? 0) > 0
                    )
                    .map((candidate) => candidate.server.game as Game)
            );
            if (!choices.size) return false;
            options.set(map, choices);
        }
        // There are two supported games: single-game maps reserve that game's
        // slots, and maps available in either game use any remaining slot.
        return (
            games.every(
                (game) =>
                    [...options.values()].filter(
                        (choices) => choices.size === 1 && choices.has(game)
                    ).length <= (slots[game] ?? 0)
            ) && maps.size <= games.reduce((total, game) => total + (slots[game] ?? 0), 0)
        );
    }
    if (!canComplete(candidates, counts, requiredMaps)) {
        throw new Error(
            "Increase the instance counts to cover every selected file's map scope, or choose servers in advanced options."
        );
    }
    const selected: string[] = [],
        slots = { ...counts };
    let maps = requiredMaps;
    for (let index = 0; index < candidates.length; index++) {
        const { server } = candidates[index],
            game = server.game as Game;
        if (!slots[game]) continue;
        const nextSlots = { ...slots, [game]: slots[game]! - 1 },
            nextMaps = new Set(maps);
        if (server.map) nextMaps.delete(server.map);
        if (!canComplete(candidates.slice(index + 1), nextSlots, nextMaps)) continue;
        selected.push(server.name);
        slots[game] = nextSlots[game];
        maps = nextMaps;
        if (games.every((game) => !slots[game])) break;
    }
    return selected;
}